1. Field of the Invention
The present invention relates to a communication apparatus to be connected to an Integrated Services Digital Network (ISDN) network.
2. Related Background Art
In a G3 facsimile machine connected to a public network for transmitting an image signal by an analog signal, it is not permitted to simultaneously effect communication by a telephone set and facsimile communication. However, in an ISDN network, it is permitted to connect a plurality of communication terminals such as telephone sets and facsimile machines to buses, and connect a communication terminal having both telephone and facsimile functions to each terminal to permit simultaneous communication by the telephone set and the facsimile machine.
FIG. 2A shows a basic interface of a common ISDN network. Numeral 21 denotes a telephone set and numeral 22 denotes a facsimile machine. In this basic interface, up to eight communication terminals may be connected. In FIG. 2B, a telephone set 21 and facsimile machines 23 and 24 with telephone sets are connected to the basic interface of the ISDN network.
In such a configuration, in many cases, the telephone set and the facsimile machine have the same address. However, at the initial connection stage in the ISDN, there is a step to inform the type of terminal to each other to keep consistency in a communication protocol, and hence it is not permitted to switch from the telephone set to the facsimile machine, as opposed to the G3 facsimile machine. Accordingly, if it is desired to switch to the facsimile machine of the same address during the speech by the telephone set in the ISDN network, it is necessary to place the telephone set on hook and then manipulate to connect the line to the facsimile machine. When it is desired to transmit a signal to the facsimile machine during the speech by the telephone set, it is necessary to redial from a sending station and designate the address (number) even if the address of the facsimile machine is same as that of the telephone set under connection.